# Upwelling Upwelling is the rise of cold, nutrient-rich [[Water|water]] from depth to the surface. It happens wherever surface water is pushed away and something must replace it — most reliably along coasts where the wind blows parallel to the shore and [[Ekman_transport]] carries the surface layer offshore. The replacement comes from below, through the [[Thermocline]] — cold, dense, and loaded with what the surface has run out of. ## Microsim — p5.js Sidecar: `Upwelling.p5.js` · route leaf: `microsim/p5js/Upwelling__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `wind slider` | alongshore wind, either direction | | `stratification slider` | thermocline sharpness | | `[h]` | switch hemisphere | *What to watch:* Blow the wind along the coast and watch the thermocline tilt up against the shore, cold water surfacing. Flip the wind and it presses down instead. ## A coastline, a wind, and a right angle The wind does not need to blow offshore. Because Ekman transport runs 90° from the wind, an alongshore wind is enough — and which direction upwells depends on the hemisphere, which is why the productive coasts are the eastern boundaries of oceans: Peru, California, Namibia, Morocco — a [[Coriolis_force|hemisphere]] rule. Reverse the wind and the same [[Vorticity|mechanism]] runs backwards as downwelling, pushing surface water against the coast and pressing the thermocline down. ## Why it feeds everything Sunlight is abundant at the surface and nutrients are not, because sinking particles export them downward continuously — a [[Diffusion|transport]] imbalance the circulation has to fix. Upwelling closes that loop, and the result is disproportionate: a few per cent of ocean area supplies a large share of the world's fish catch, which makes this an [[Ecosystem|ecological]] argument as much as a [[Fluid_dynamics|fluid]] one. It is also why El Niño years are economically brutal on the Peruvian coast — the [[Thermocline|thermocline]] deepens, the upwelled water comes from above it instead of below, and the nutrients simply are not there even though the wind still blows. **Reads with:** *Introduction to Physical Oceanography (Robert H. Stewart, 2008)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/introduction-to-physical-oceanography) · [download](https://github.com/introocean/introocean-en/releases/tag/v20200229) · CC BY-NC-SA. Section 7 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Ekman_transport]] · [[Thermocline]] · [[Ocean_current]] · [[Coriolis_force]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Upwelling) : [Wikitube](https://en.wikitube.io/wiki/Upwelling) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*